1. Field of the Invention
The present invention relates to an electrochemical reactor including an electrolytic refining device, a practical battery and capacitor, which utilizes resistance to fluid pressure of a liquid-repellent porous membrane.
2. Description of the Related Art
The base metal elements belonging to Group 1, Group 2 and Group 13 of the periodic table are ionized upon contacting water and immediately self-discharge, producing hydrogen. For this reason, these metal elements must be strictly prohibited from contacting water. Thus, as electrolytic refining to deposit these, there is no other production method than a molten salt electrolysis. In the practical batteries, there are no primary or secondary batteries which use an electrolyte solution with respect to Ca, Ba or Sr, which belongs to Group 1 or 2 of the periodic table. Further, there are primary batteries with respect to Be, Mg of the Group 2 elements, or aluminum, which is a Group 13 element of the periodic table, but there is no secondary battery with respect to these elements. As the secondary batteries, which include lithium ion batteries and sodium ion batteries of Group 1 elements, a nonaqueous electrolyte solution (organic electrolyte) or a solid electrolyte has been developed. Further, for a battery using sodium of Group 1 element, a sodium sulfur battery (NS battery), which operates at a high temperature of 300° C. or higher and uses sodium as a molten salt electrolyte, has been developed.
For practical batteries, a lighter electrode material, a higher electromotive force and a larger discharge capacity are presently in demand. Therefore, elements of Group 1 of the periodic table are ideal negative electrode materials, but it is difficult to avoid self-discharge. The reason why these practical batteries, electrolytic refining and capacitor causes self-discharge is that a negative electrode and a positive electrode are present in the same electrolyte solution. Under these circumstances, there are urgent technical developments in demand to inhibit self-discharge by separating the electrolyte and electrodes, and also to interrupt a base metal element of Group 1, 2 or 13 of the periodic table and water from each other.
For capacitors for power storage (capacitor), a larger capacity and a more rapid charge and discharge are desired. As a capacitor which fills these, an electrochemical capacitor is ideal, such as an electric double layer capacitor, a redox capacitor or a hybrid capacitor. Drawbacks of these capacitors are high leak current and self-discharge. Under these circumstances, there is an urgent technology development in demand to suppress the leakage current.
The self-discharge is a phenomenon in which the metal of the negative electrode dissolves and at the same time, electrons and hydrogen ions generated react with each other to produce hydrogen, with the result that the electrons do not move to the positive electrode, and thus current does not flow. As a general method of suppressing self-discharge in an aqueous electrolyte solution, Patent Literature 1 discloses that a nickel-based porous body is provided on a positive electrode for an alkali-storage battery, and the porous body is filled with particles of an active material which contains nickel and additives, thereby reducing self-discharge. Patent Literature 2 discloses a method of suppressing self-discharge by setting of such a shape of electrode that does not decrease the real reaction area even if the opposing area of the alkali storage battery electrode is increased. Patent Literature 3 discloses a long-life alkaline battery comprising, as a separator, a multi-layer member of a sheet comprising fibers containing sulfonated polyolefin resin fibers as a principal component, and a sheet subjected to a hydrophilization treatment other than sulfonation, with less self-discharge and high capacitance retention. Patent Literature 4 discloses an electrode for lithium batteries in which active material thin films which adsorb/release lithium, such as a microcrystal silicon thin film and an amorphous silicon thin film are provided on a charge collector via an interlayer. Patent Literature 5 discloses that as an electrode active material in a lithium battery, porous lithium titanate is excellent in the nonaqueous electrolyte impregnating properties and improves charge/discharging cycle characteristics. Patent Literature 6 discloses a sodium secondary battery comprising a positive electrode of a carbon-based positive electrode active material which can adsorb and release anions, and a negative electrode of a negative electrode material which can adsorb and release Na, which is, such as Sn or Zn. As to sodium sulfur batteries, in which sodium is molted, an atmosphere temperature of 300° C. is required to form a molten salt. But, Patent Literature 7 discloses the operation of a battery at an atmosphere temperature within a range of 60 to 130° C., which can be achieved by using a molten salt composite containing two or more types of molten salts MFSI comprising bisfluorosulfonylimide (FSI) for anions and alkali metal M for cations.
As to the isolation film between an electrolyte and an electrode, Patent Literature 8 discloses that a polyolefin microporous membrane having a pore diameter of 0.1 μm or less has thermal stability and therefore it is suitable as a separator for a high-capacity/high-output battery. Patent Literature 9 discloses that a scale-like inorganic porous membrane of silica, alumina or the like is provided on a positive electrode, a negative electrode or a separator, and thus the performance of a battery can be retained without degrading the ionic conductance. Patent Literature 10 discloses that an isolation film used for a nonaqueous secondary battery is a thermal-resistant porous membrane containing chlorine, or a multi-layered film of a thermal-resistant resin and porous polyolefin, or a multi-layered film of a layer including a thermal-resistant resin and a porous polyolefin.
As to the use of a water-repellent porous membrane, Patent Literature 11 discloses a fluorine-based water-repellent porous membrane having a porosity of 60 to 90% and an air permeability of 20 seconds or less is used in a solid polymer fuel cell. Patent Literatures 12, 13 and 14 each discloses a method of manufacturing a fluorine-based water-repellent porous membrane by irradiating a fluorine-based water-repellent porous membrane with an excimer laser beam in the presence of a compound comprising an atom and a hydrophilic group and having a bond energy therebetween of 128 or more kcal/mol. Further, Patent Literature 15 discloses a method of manufacturing a three-dimensional cell culture element for patients suffering from Parkinson's disease, Alzheimer disease, diabetes, osteomalacia and the like, in which inner pores of a fluorine-based water-repellent porous membrane are substituted with hydrophilic groups by photo-reaction caused by ultraviolet radiation, and dopamine-producing cells, fibrocytes, collagen production-promoting cells, stem cells, nucleus-pulposus cells, insulin-producing cells, etc. are cultured in the inner walls of the pores, which exhibit the hydrophilic properties. Furthermore, Masataka Murahara et al. reports in Non-patent Literature 1 that the water-resistant pressure of a water-repellent porous fluorine-based resin film with a pore diameter of 33 μm is 1500 torr, but the insides of the pores are photo-modified to be hydrophilic to lower the water-resistant pressure to 20 torr, and the thus modified film is used in an aqueous-humor regulating valve for glaucomatous patients.